A circular saw cutting machine of this type reduces the rotation of an electric motor through a pulley and a gear mechanism provided in a gear box and transmits the reduced rotation to a main shaft, has a circular saw attached to one end of the main shaft which end protrudes from the gear box, rotates the main shaft at a low speed with a high torque and thereby cuts a metallic work material. Since the circular saw cutting machine uses gears in a rotation transmission section as stated above, the backlash of gears occurs. Due to this, at the start region and end region of cutting a work material for every cutting operation with the circular saw, with the number of cutting related teeth Zi being in a range of 0 to 1.0, when the saw tooth is bit into and pulled out of the work material, the rotational variation corresponding to the backlash of the gears occurs. Also, with the number of cutting related teeth Zi being high, a regenerated chatter which is a self-excited vibration in the feed direction of a main body of the machine accompanied by the rotational variation of the gears often occurs. The rotational variation of the gears causes chatter vibration in the circular saw and deteriorates cutting accuracy. At the same time, the damage, failure and the like of a tip shortens the service life of the circular saw. Further, vibration and noise deteriorate working environment.
In a circular saw cutting device designed to prevent such rotational variation of the gears, as shown in, for example, Japanese Utility Model Examined Application Publication No. 62-28334, pressing pieces are provided on both sides of the circular saw, one of the pieces actuating a hydraulic cylinder to thereby apply a frictional force before the start of cutting operation. Thus, cutting operation is started while eliminating the backlash of a power system and the frictional force is removed by a timer during the operation. According to another circular saw cutting device, as shown in Japanese Utility Model Examined Application Publication No. 7-48339, a control shaft is directly coupled to a main shaft, to which a circular saw is attached, through a gear and a braking device is provided at the control shaft. According to this circular saw cutting device, from the start to the end of cutting operation by means of the circular saw, the backlash of the gears of a drive system is suppressed while a braking force is electrically controlled by a solenoid proportional valve, thereby eliminating the chatter vibration of the circular saw during the cutting operation.
The above-stated circular saw cutting device is, however, designed to apply a braking force to the driving system at the start and end of the cutting operation to thereby forcedly eliminate the backlash of the gears and to perform the cutting operation while reducing cutting power. Owing to this, the mechanical structure is complicated and an electric control structure is required, with the result that the machine disadvantageously becomes expensive and the maintenance of the machine requires more labor.
The present invention has been made to solve the above disadvantages. It is, therefore, an object of the present invention to provide a circular saw cutting machine capable of eliminating the chatter vibration of a circular saw during cutting operation to thereby enhance cutting accuracy, prolonging the service life of the circular saw and suppressing the occurrence of noise at low cost.